I’ve designed a few M.2 adapters for my own and my friends’ use, and having found those designs online, people have asked me for custom-made adapters. One of these requests is quite specific – an adapter that adds one more PCIe link to an E-key M.2 slot, the kind of slot you will see used in laptops for WiFi cards.
See, the M.2 specification allows two separate PCIe links connected to the E-key slot; however, no WiFi cards use this apart from some really old WiGig-capable ones, and manufacturers have long given up on connecting a second link. Nevertheless, there are some cards like the Google Coral M.2 E-key dual AI accelerator and the recently announced uSDR, that do indeed require the second link – otherwise, only half of their capacity is available.
It’s not clear why both Google and WaveletSDR designed for a dual-link E-key socket, since those are a rare occurrence; for the Google card, there are plenty of people complaining that the board they bought just doesn’t fully work. In theory, all you need to do to help such a situation, is getting a second PCIe link from somewhere, then wiring it up to the socket – and a perfect way to do it is to get a PCIe switch chip. You will lose out on some bandwidth because the uplink PCIe connection of the switch can only go so fast; for things like this AI accelerator, it’s not much of a problem since the main point is to get the second device accessible. For the aforementioned SDR, it might turn out useless, or you might win some but lose some – can’t know until you try! Continue reading “PCIe For Hackers: An M.2 Card Journey”→
With DisplayPort, the I2C bus we’ve always seen come bundled with VGA, DVI and HDMI, is no more – it’s been replaced by the AUX bus. AUX is a 1 MHz bidirectional diffpair – just a bit too complex for a cheap logic analyzer, though, possibly, something you could wrangle with the RP2040’s PIOs. Hacking thoughts aside, it’s a transparent replacement for I2C, so that software doesn’t have to be rewritten – for instance, it usually does I2C device passthrough over AUX, so that EDID data can still be stored in a separate EEPROM chip on the monitor or eDP LCD panel.
AUX isn’t just a differential bus, it’s more pseudodifferential, like USB2 – for instance, AUX_P and AUX_N are used separately, with a combination of 1 MΩ and 100 kΩ pullups and pulldowns signaling different states of the physical connection – for instance, a pullup on AUX+ and a pulldown on AUX- means that an external device has been connected. If you’d like to learn which combination of resistors means what, you can find in the DisplayPort specification, which isn’t distributed openly but isn’t hard to come by, either.
Also, DisplayPort link training happens over AUX, and in order to facilitate that, a piece of DisplayPort controller’s external memory is usually exposed over the AUX channel, through a mechanism that’s called DPCD. If you dig a bit, using “DPCD” as the keyword, you can easily reach into the lower-level details of your DisplayPort connection. Some of the DPCD memory map is static, and some parts are FIFOs you can funnel data into, or out of. You can find a wide variety of documents online which describe the DPCD structure – for now, here’s a piece of Bash that works on Linux graphics drivers for AMD and Intel, and will show you you the first 16 bytes of DPCD:
In particular, the 4th nibble (digit) here describes the amount of lanes for the DisplayPort link established – as you can see, my laptop uses a four-lane link. Also, the /dev/drm_dp_aux0 path might need to be adjusted for your device. In case you ever want to debug your DP link, having direct access to the DPCD memory space like this might help you quite a bit! For now, let’s move onto other practical aspects. Continue reading “DisplayPort: Under The Hood”→
When you think of driving up or down an embankment, do you ever wonder how much foam you’re currently driving on? Probably not, because it hardly seems like a suitable building material. But as explained by [Practical Engineering] in the video below the break, using an expanded material to backfill an embankment isn’t as dense as it sounds.
In many different disciplines, mating dissimilar materials can be difficult: Stretchy to Firm; Soft to Hard; Light to Heavy. It’s that last one, Light to Heavy, that is a difficult match for roadways. A bridge may be set down in bedrock, but the embankments approaching it won’t be. The result? Over time, embankment settles lower than the bridge does, causing distress for cars and motorists alike. What’s the solution?
To mitigate this, engineers have started to employ less dirty materials to build their otherwise soil based embankments. Lightweight concrete is one solution, but another is Expanded Polystyrene (EPS) foam. Its light weight makes installation simple in anything but a strong breeze, and it’s inexpensive and durable. When used properly, it can last many years and provide a stable embankment that won’t settle as far or as quickly as one made of dirt. Because as it turns out, dirt is heavy. Who knew?
Folding phones are all the rage these days, with many of the major smartphone manufacturer’s having something in this form factor. Apple has been conspicuously absent in this market segment, so [KJMX] decided to take matters into their own hands with the “iPhone V.” (YouTube – Chinese w/subtitles via MacRumors).
Instead of trying to interface an existing folding phone’s screen with the iPhone, these makers delaminated an actual iPhone X screen to use in the mod. It took 37 attempts before they had a screen with layers that properly separated to be both flexible and functional. Several different folding phones were disassembled, and [KJMX] found a Motorola Razr folding mechanism would work best with the iPhone X screen. Unfortunately, since the iPhone screen isn’t designed to fold, it still will fail after a relatively small number of folds.
Other sacrifices were made, like the removal of the Taptic Engine and a smaller battery to fit everything into the desired form factor. The “iPhone V” boasts the worst battery life of any iPhone to date. After nearly a year of work though, [KJMX] can truly claim to have made what Apple hasn’t.
We take shortcuts all the time with our physical models. We rarely consider that wire has any resistance, for example, or that batteries have a source impedance. That’s fine up until the point that it isn’t. Take the case of the Navy’s Grumman F11F Tiger aircraft. The supersonic aircraft was impressive, although it suffered from some fatal flaws. But it also has the distinction of being the first plane ever to shoot itself down.
So here’s the simple math. A plane traveling Mach 1 is moving about 1,200 km/h — the exact number depends on a few things like your altitude and the humidity. Let’s say about 333 m/s. Bullets from a 20 mm gun, on the other hand, move at more than 1000 m/second. So when the bullet leaves the plane it would take the plane over three seconds to catch up with it, by which time it has moved ever further away, right?
There’s no denying that while railroads have switched to diesel and electric as their primary power sources, there’s a certain allure to the age of steam. With that in mind, a group of Pennsylvania train fans are bringing the alleged fastest steam train back from extinction.
It takes real dedication to build a 428-ton device from scratch, but these rail aficionados seem to have it in spades. Armed only with the original blueprints and a lot of passion, this team has already finished construction of the boiler and nose of the Class T1 replica which is no small feat. This puts the train at approximately 40% complete.
Some changes are planned for the locomotive including a change to fuel oil from coal and replacing the poppet valves prone to failure with camshaft-driven rotary valves. While not original hardware, these changes should make the train more reliable, and bring the world record for the fastest steam locomotive within reach. If the T1 replica can reach the 140 MPH storied of the originals, it will smash the current record of 126 MPH held by a British train, the A4 Mallard, which would be exciting indeed.
Speaking of Pennsylvania and steam, a trip to Scranton is a must for anyone interested in the age of rail.
In the electronics world, even for the hobbyists, things have only gotten smaller over the years. We went from through-hole components to surface mount, and now we’re at the point where the experienced DIYers are coming around to the idea of using ball grid array (BGA) components in their designs. We’d wonder what things are going to look like in another couple decades, but frankly, it gives us the heebie-jeebies.
So while we’re pretty well versed these days in the hows and whys of tiny things, we see comparatively little large-scale engineering projects. Which is why we were excited to have Andy Oliver stop by this week for the Heavy Engineering Hack Chat. His day job sees him designing and inspecting the control systems for movable bridges — or what many would colloquially refer to as drawbridges.
Now you might think there’s not a lot of demand for this particular skill set, but we’re willing to bet there’s a lot more of these bridges out there than you realized. Andy kicked things off with the revelation that just between the states of Florida and Louisiana, there are about 200 movable bridges of various sizes. On a larger scale, he points out that BridgeHunter.com lists an incredible 3,166 movable bridges in their database, though admittedly many of those are historical and no longer standing. (There really is a site for everything!)
Andy Oliver
There’s also a huge incentive to keep the existing bridges functioning for as long as possible — building a new one these days could cost hundreds of millions of dollars. Instead, repairs and upgrades are the name of the game. Andy says that if it’s properly maintained, you should get about a century out of a good bridge.
It will probably come as little surprise to find that keeping things as simple as possible is key to making sure a movable bridge can withstand the test of time. While we might imagine that all sorts of high-tech automation systems are at work, and they probably would be if any of us were in charge, Andy says that most of the time it’s old school relay logic.
Even controlling the speed of motors is often down to using beefy relays to switch some additional resistance into the circuit. But when reliability and ease of repair are top priorities, who’s to argue against a classic? Andy recalled a time when a government client made it clear that the only tool you should need to maintain a particular bridge’s control system was a hammer.
Of course, when moving around a million pounds of steel, there’s more than just electrical considerations at play. You’ve also got to take into account things like wind forces on the bridge, specifically that your gears and motors can handle the extra load without tearing themselves apart. The bridge also needs an emergency stop system that can arrest movement at a moment’s notice, but not damage anything in the process.
A lot of fascinating details about these motorized behemoths were covered in the Chat, so we’d invite anyone who’s ever watched a bridge slowly reconfigure itself to peruse through the full transcript. Special thanks to Andy Oliver for stopping by and sharing some of the details about his unique career with the community, and remember that if you’ve got your own engineering stories to tell, we’d love to hear them.
The Hack Chat is a weekly online chat session hosted by leading experts from all corners of the hardware hacking universe. It’s a great way for hackers connect in a fun and informal way, but if you can’t make it live, these overview posts as well as the transcripts posted to Hackaday.io make sure you don’t miss out.
